Optical waveguide chips are used to branch or couple light that propagates through optical fibers and other light transmitting media. For example, an embedded type of optical waveguide chip has, on a substrate, formed of Si, etc., a polymer optical waveguide layer, which includes a core that guides light and a cladding that covers the core. Such optical waveguide chips are manufactured, for example, by the following method. First, a lower cladding layer is formed on a Si wafer. A core layer, with a higher refractive index than the lower cladding layer, is then formed to an arbitrary planar shape on the lower cladding layer by a photolithography technique or an etching technique. An upper cladding layer is then formed so as to cover the core layer. Optical waveguide chips are then obtained by cutting the Si wafer, on which the lower cladding layer, the core layer, and the upper cladding layer have been formed, along predetermined lines into chips.
As an art for cutting a Si wafer into chips in a method of manufacturing such optical waveguide chips, there is, for example, an optical waveguide chip manufacturing method disclosed in a Patent Document 1. FIG. 1 is a diagram for explaining this method. In this method, after an optical waveguide 102 is formed on a wafer substrate 101, parts of the optical waveguide 102 and the substrate 101 are cut by a dicing blade 103. By this cutting, an end surface 102a of the optical waveguide 102 is formed, and a step 101b, having a side surface that is coplanar to the end surface 102a of the optical waveguide 102, is formed on the substrate 101. In the Patent Document 1, it is indicated that abrasive grains, formed by the cutting of the substrate 101, become fine particles by being pulverized finely between the substrate 101 and the dicing blade 103, and an action of polishing the optical waveguide end surface 102 is provided by the fine particles. It is also indicated in the Patent Document 1 that when full-cut dicing of the substrate (cutting of the substrate fully in a thickness direction) is performed by the dicing blade 103, larger chipping (nicking) occurs in comparison to performing half-cut dicing (cutting of the substrate partially in the width direction and leaving of a portion of the substrate in the width direction) by the dicing blade 103 and consequently, the optical waveguide end surface becomes flawed and the optical waveguide becomes peeled readily. The manufacturing method according to the Patent Document 1 thus intends to form a better optical waveguide end surface by controlling the polishing action by the abrasive grains according to the depth of cutting of the substrate by the dicing blade 103.    Patent Document 1: Japanese Patent Application Laid-Open No. H11-337757